Feeding mechanically dried coal slurry from a centrifuge bowl



1966 v. z. CARACRISTI FEEDING MECHANICALLY DRIED COAL SLURRY FROM A CENTRIFUGE BOWL Filed June 15, 1962 F l G I Saw/W INVENTOR VIRGINIUS Z- CARACRSTI m ws/w, M

FIG-4 ATTORNEY United States Patent 3,233,566 FEEDING li EECHANICALLY DRIED CGAL SLURR FROM A CENTT-HFUGE EGWL Virginius Z. Caracristi, West Hartford, (Iona, assignor 'to Combustion Engineering, Inc., Windsor, Conn, a corporation of Delaware Filed June 15, 1962, Ser. No. 202,364 2 Ciaims. (til. 110-106) This invention relates to feeding coal slurry and particularly to feeding the partially dewatered slurry from a centrifuge.

An obiect of this invention is mechanism improving the feeding of the output of a centrifuge from the centrifuge to a receiving station.

A further object is a combined centrifuge and fun.

A still further object is mechanism mixing heated air from -a pulverizer with partially dewatered coal from a centrifuge and blowing the mixture into the pulverizer.

A still further object is a centrifuge for coal slurry Whose coal discharge section comprises a fan for blowing the'coal away from the centrifuge and includes means introducing heated air into, and the centrifuge forcing coal into, the fan.

Otherobjects and advantages willb'e apparentfrom the following specification and the :attached drawings in which:

FIGURE 1 is an elevation of the system including the centrifuge and pulverizer;

FIGURE 2 is a detail sectional elevation of the centrifuge discharge section and fan;

FIGURE 3 is a sectional end view of the fan andcentrifuge; and

FIGURE 4 is an enlarged sectional view of the fan blade and casing.

Coal crushed "at the mine and mixed with a liquid such as water to form 'aslurry may be transported by means of a pipeline and pumps over long distances to a receiving station where it may be dried or partially dried and fed to "a furnace for burning. The present invention relatesto "an improved method'and means of heating and transporting the partially dewatered coal slurry, known as filter cake, from the centrifuge used for dewatering the slurry to a receiving station such as a pulverizen a thermo drying unit, or directly to the furnace.

The filter cake has a consistency somewhat like a thick mud and has a tendency to sometimes stick or accumulate on the transporting mechanism such as the belt or centrifuge housing or the ducts or pipeline directing the filter cake from the centrifuge. This sticking or accumulation may produce irregular feeding by starving the furnace at times and then suddenly releasing some or all of the accumulation to provide a mixture too rich in coal and tending to produce inefiicient combustion. More uniform feeding of coal from the centrifuge to the pulverizing mill and to the burners is highly desirable and is the improvement provided by the present invention.

For purposes of explanation this invention is shown as incorporated in a mechanical dewatering system in which the coal slurry is fed to a centrifuge indicated generally at through a pipe or shaft 12. This centrifuge, which may be a standard commercial article such as a centrifuge manufactured by the Bird Machine Company of South Walpole, Massachusetts, modified to incorporate the present invention, comprises a hollow drum 14 in the form of a cone frustum adapted to be rapidly rotated as by a motor 16 and having a substantially imperforate outer surface except for discharge openings 18 at the small end of the frustum. Although these discharge openings 18 have been shown as spaced from the end of the drum it should be understood that they may be placed adjacent to the end of the drum if desired. The

drum has closed ends except for the discharge openings for liquid in the large end 20 spaced inwardly from the outer surface of the frustum and a central opening in the large end 2t) at the axis of the frustum for receiving slurry through the pipe or shaft 12 from the pipeline conveyor. ,A casing 22 surrounds the rotating frustum and contains one or more partitions 24 dividing the easing into two discharge chambers one of which, 26,. discharges solids into duct or pipe 28 and the other, not shown, discharges liquids into receiver 30 and pipe 32.

The slurry discharged into the interior of the frustum through pipe 12 collects at the large end of the frustum and it is thrown outwardly by centrifugal force. A screw conveyor 34 is rotated, by meansof gears in a gear box 36, relative to the frustum and cooperates with the interior of the frustum as the tfiustum rotates relative to the screw conveyor to force coal from the large end toward the small end of the frustum where it is discharged through the orifices 18. Water, being 'lighter than the coal, will tend to stay nearer the axis of the centrifuge as the coal is .pressed, squeezed or forced against the drum and will be discharged through the orifices in the large end 20 of the frustum. The coal, which still may contain 20% or less of moisture is centrifugally discharged with consider able force from the orifices 18. Fan blades or paddles 38 are mounted on the exterior of the drum 14 preferably adjacent an orifice 18 and are secured to the drum by any suitable means such as welding and/or braces or supports 40. A fan or blower casing 420i generally volute section surrounds the small end of the drum 14 and encloses the fan or blower blades 38 to thus convert the small end of the centrifuge drum into a blower. The partition 24., which is sealed at 46 with respect to "the rotating drum 14, a portion of casing '22}, and the end 48 of the casing 22, which is sealed at 50 with-respect to the supporting shaft .52, form a sealed chamber 26 surrounding the casing 42. The fan casing 42. has an exit opening 'or duct 28 extending through the centrifuge casing 22. :Brackets 54 extending between the casings .22 and '42 support the casing 42 from the casing 22. The drum 14 thus acts as a hub for the fan or blower blades 38 land air inlet passages or openings 56 in the ends of the blower casing 42 and adjacent the hub or drum l4 admitair to the blower casing adjacent the coal exits 18 where the air is mixed with the filter cake, or partially dewatered .slurry, being forcefully ejected through the discharge openings 18. This air which may be heated air is introduced into the sealed chamber 26 surrounding the fan housing 42 by means of a conduit 60 or a conduit 62. This heated air mixing with the filter cake serves to further dry the filter cake and by reason of the blower action and high velocity of the air fiow through the exit 23 will overcome the tendency of the filter cake to stick to the housing 42 or the conduit 28 and will force the filter cake from the centrifuge in a uniform flow pattern.

The filter cake discharged from the centrifuge may be fed to a thermo drying unit, directly into the furnace, or as shown for purposes of explanation in this application continuously into a pulverizing mill indicated generally at 64. The pulverizing mill which may be a standard commercial bowl mill receives the filter cake or dewatered slurry, discharged from duct 28, in a rotating bowl 66. As the bowl rotates it passes by, and carries the coal under, a spring pressed roller 68 which crushes and pulverizes any coal lumps remaining in the slurry. Heated air is drawn into the exhaust fan 70 through a pipe or duct 72. This air which is normally heated mill air is further heated as by a gas heater fed through line 74. This heated air in passing through the bowl mill further dries the coal and also acts to convey the coal through the mill and out through duct 76, exhaust fan 70, and discharge 3 duct 78 to the burner 80 in the furnace 82. Secondary air may be supplied to the burner in the usual manner, not shown. The motor 84 supplies power for the bowl mill 64 and the exhaust fan 70.

The heated air supplied to the sealed chamber 26 through the ducts 60 and 62 may be selectively controlled by suitable valves 86 and 88. The air supplied to the duct 60 may be heated by any suitable means not shown such as a gas burner, a heat exchanger, or it may be mill air. The heated air supplied through duct 62 is taken from the pulverizer 64. Air forced through the pulverizer mill 64 under the influence of fan 70 draws the coal dust upwardly around the outside of classifier 89 and in through openings adjacent the top of the classifier Where the air and coal dust is given a whirl or a swirling motion or a cyclone action which will force the heavier particles of coal towards the outer surface of the inside of the cone shaped classifier 88 and the finer particles and dust will be drawn off of the center of the swirling mass and fed to the furnace 82. Due to restrictions inside of the cone 89 and the air flow pattern of the classifier the air flow through the center of the cone is less than around the outside and the larger particles will gravitate back through the opening in the bot tom of the cone and into the bowl for further pulverizing. While the heated air taken from the pulverizer for recirculation may be taken from any suitable portion of the pulverizer it now is preferred to take this air from the low pressure region in the air passage between the outside of the large diameter of the classifier 89 and the inside of the pulverizer casing. At this point in addition to the heated air some pulverized coal may also be carried back to the sealed chamber for mixing with the filter cake being discharged by the centrifuge. This coal dust by reason of its having been mixed with the heated air in the pulverizer is dryer than the product of the centrifuge and when miXed with the filter cake from the centrifuge will assist in further drying the filter cake and assist in its transport to the pulverizer mill.

While a bowl mill has been shown in the drawing and described in the specification it should be understood that any suitable type of pulverizer may be used for pulverizing the slurry discharged by the centrifuge. Whatever type of pulverizer is used provision should be made for the further drying of the centrifuge discharge preferably by a blast of hot air passing through the mill which will act to dry and transport the pulverized coal or coal dust. This air blast can be supplied by the exhaust fan such as exhaust fan 70 or it can be supplied by a pressure fan supplying air under pressure to the duct 72 supplying air to the pulverizer or if desired both a pressure fan and an exhaust fan may be used. A suitable type of bowl mill is shown in Patent Number 2,848,- 170 issued to I. Crites on August 19, 1958 and a suitable type of beater mill is shown in Patent Number 2,985,390 issued to P. Raetz on May 23, 1961.

The above combined centrifuge and blower mixing heated air or heated air and coal dust with the filter cake product of the centrifuge and continuously blowing the mixture through a discharge opening or a duct 28 away from the centrifuge will provide a more positive, and a substantially uniform, flow of filter cake from the centrifuge to any desired receiving station such as a pulverizing mill or if desired directly to a furnace or to a thermo heating and drying unit.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departing from its spirit and that various changes can be made which would come within the scope of the invention which is limited only by the appended claims.

I claim:

1. A centrifuge for separating coal and water from a coal slurry including, a rotating drum having a coal discharge opening, a casing having an air inlet passage and surrounding said drum and opening and receiving coal discharged from said opening and means drawing air into, and forcing coal and air out of, said casing, a pulverizer receiving the discharged coal and air from said coal and air forcing means means directing heated air through said pulverizer and means directing heated air from said pulverizer to said air inlet of said casing.

2. A combination as claimed in claim 1 in which the pulverizer includes pulverizing mechanism and a classifier and the air directing means takes air and pulverized coal from between said pulverizing mechanism and said classifier and directs said air and pulverized coal to said inlet.

References Cited by the Examiner UNITED STATES PATENTS 2,103,453 12/1937 Graemiger 110- 106 2,148,981 2/1939 Dundas et al. 11015 2,213,668 9/1940 Dundas et al. 1l015 2,346,151 4/1944 Burk 1107 3,073,652 1/1963 Reichl 30266 3,081,026 3/1963 Lacher et al. 233-7 FREDERICK L. MATTESON, JR., Primary Examiner.

KENNETH W. SPRAGUE, JAMES W. WESTHAVER,

Examiners. 

1. A CENTRIFUGE FOR SEPARATING COAL AND WATER FROM A COAL SLURRY INCLUDING, A ROTATING DRUM HAVING A COAL DISCHARGE OPENING, A CASING HAVING AN AIR INLET PASSAGE AND SURROUNDING SAID DRUM AND OPENING AND RECEIVING COAL DISCHARGED FROM SAID OPENING AND MEANS DRAWING AIR INTO, AND FORCING COAL AND AIR OUT OF, SAID CASING, A PULVERIZER RECEIVING THE DISCHARGED COAL AND AIR FROM SAID COAL AND AIR FORCING MEANS MEANS DIRECTING HEATED AIR THROUGH SAID PULVERIZER AND MEANS DIRECTING HEATED AIR FROM SAID PULVERIZER TO SAID AIR INLET OF SAID CASING. 